The present invention relates to separation of plasma or serum from the red cells of a blood sample and more particularly to an apparatus and method for rapidly achieving such separation.
In current practice plasma or serum is typically separated from the red blood cells of a blood sample by placing whole liquid or clotted blood respectively, in a tube, placing the tube in a swinging bucket type centrifuge which upon activation rotates rapidly and causes the tube to acquire a horizontal position. The red cells being heavier than the plasma or serum migrate to the end of the tube furthest from the center of rotation thus producing separation of the various components of the sample.
The above procedure is time consuming requiring extended periods of centrifuging to achieve the desired results because of the long migration path of the red cells.
U.S. Pat. No. 3,190,547 to J. J. Shanley discloses in FIGS. 10-13 a centrifuge wherein bottles are located below evacuated plasma receivers. The combination of each bottle and receiver is rotated together with other such combinations about an axis parallel to the axis of each combination, which axis passes through a bottle and receiver. In consequence red cells migrate upon rotation of the bottles about such axis toward the outer walls of the sample bottles. Upon completion of centrifuging the sample bottle and plasma receivers are connected through hollow needles situated in self-sealing stoppers in each member of the combination. The plasma is drawn into the plasma receivers which are then spun at a higher than previous rotational velocity separately from the now stationary specimen bottles to produce further separation of the materials drawn therein.
The mechanism is very complex requiring two separately driven rotating shafts, two different hollow needles to affect interconnection of the bottle and the receiver, rectangular shaped or other non-cylindrical specimen bottles to ensure that the bottles do not rotate about their own axes. This procedure further requires proper registration of the needle with the sample bottle. To provide proper alignment with the various strata in the specimen bottle, a readily movable self-sealing stopper in the specimen bottle is employed to assist in the search for the strata of the material desired. This procedure may require opening of the specimen bottle to locate the strata interface thus compromising the sterility of the specimen and possibly endangering the workers.
It is an object of the present invention to greatly shorten the time required to separate the components of either anticoagulated and/or clotted blood samples.
It is another object of the present invention to produce separation of the red blood cells from other components of whole blood in a system in which the plasma or serum at the end of the process is disposed in a separate container from the red cells.
Still another object of the present invention is to automatically separate serum or plasma into a different container from red blood cells from which the serum or plasma has been extracted.
Still another object of the present invention is to provide a quite simple assemblage for application to a centrifuge, the assemblage comprised of two test tubes, with self-sealing stoppers, a two ended hollow needle and a universal fixture to hold the tubes and needles in proper coaxial registration.
Yet another object of the present intention is to provide an apparatus for rapidly separating plasma or serum from blood samples by an assembly having a fixed structure of small size employing standard test tubes of the type employed by medical and paramedical personnel to withdraw blood from a patient.
It is another object of the invention to provide a fixture for holding the assemblage in registration, the fixtures all having a universal interface for registration with a centrifuge designed for such purpose and having a second interface that varies only with the dimensions of the test tubes. Thus loading and unloading of the centrifuge is simple and lends itself to automated input to and output from the machine. Also such arrangement increases safety by reducing the contact of laboratory personnel with the equipment and the danger of contact with potentially contaminated blood.
The preferred embodiment of the present invention is comprised of a spinning drum, which spins a plurality of pairs of head-to-head tubes held coaxially of one another and located around a vertical axis parallel to and spaced from the longitudinal center line of the tubes. Each pair of tubes is arranged head to head in which a primary tube contains blood while a collection tube is under vacuum and is empty. The primary or sample tube is located below the collection tube.
When the drum rotates, the red cells migrate a quite short distance to one side of the primary or sample tube. The separation time is quite short because of the shorter separating distance compared to the present method in which the cells are driven to the bottom of a tube, or in the Shanley patent to the walls of a 500 ml bottle. There is less chance of damage to the red cells due to the smaller radial pressure required. The use of small vessels such as test tubes has the advantage of more uniform pressure across the tube and thus a calculated maximum force may be employed without fear of damage to the specimens. Large vessels do not permit uniform pressures across the vessels so that lower average forces must be employed to insure that excessive pressure is not developed in the sample. Also in larger vessels separation may not be uniform as a result of non-uniform pressure.
The two tubes of each pair, in accordance with the present invention, the sample and collection tubes, are connected during the interval the drum is rotating by a single two sided hollow needle. The needle is introduced into the center of each of the tubes through self-sealing stoppers substantially simultaneously.
The plasma flows into the collection tube by reason of the partial vacuum in the collection tube and the pressure developed by the centrifuging action in the primary tube. It is to be noted that in humans the red cell and other non-plasma or serum volume of blood represents about 44% in males and 41% in females. The sample tube is usually not completely filled, 80% to 90% being the usual. At 90% with 44% red cells, only about 40% of the tube contains red cells thus providing a reasonable margin of safety. With a 41% red cell sample only 37% of the tube is filled with red cells. Thus the red cells and other non-serum or plasma materials are not near the center of the sample tube as a result of centrifuging and the two ended needle may be located along the center line of the tubes. Red cells are not available to the needle and therefore will not pass into the empty collecting tube. This feature provides a plasma or serum containing tube at the end of centrifuging suitable for use in the analytical determinations without any further serum or plasma transfer steps required. Further it is not necessary to perform any function that can compromise the sterility of the sample.
Further, in accordance with the preferred embodiment, there is a fixture which holds the two tubes facing each other and a hollow needle having two sharp ends in between. The tubes must have self-sealing stoppers or caps so that the blood flows only through the needle and does not spin out of the tubes. The tubes and needle can be snapped on or off the fixture manually or automatically. Further, the fixture with the tubes can be loaded or unloaded manually or automatically onto the drum. After the separation is completed and while the centrifuge is still spinning the two tubes are forced to slide towards each other so that the needle penetrates both stoppers allowing plasma to flow from the primary to the collection tube. The needle is preferably held by a disc that is snugly received by the fixture and may be made integral with the fixture. In all cases the needle should be a disposable item.
The collection tube can be labeled after it is placed in the fixture by any of several well known technologies such as laser printing directly onto the glass or plastic of the collection tube or on a sticky back label so that the collection tube label matches exactly a bar code or other code on a readable label previously applied to the sample tube. This approach assure positive specimen identification and replaces a step currently performed by other less dependable methods in which mislabeling of the collection tube can occur. Both tubes can be pre-labeled and the labeling verified upon insertion into the centrifuge by a computer or other suitable means.
Furthermore, the drum is provided with a plurality of bays, each of which can contain a fixture with tubes. The bay is directed inwardly opposite to the direction of rotation so that inertia forces the fixture into its designated position. The bays are designed, however, such that it is easy to replace the fixtures with the tubes by an external device that loads and unloads the centrifuge. The fixture can accommodate tubes of different sizes and different fixtures may be employed for different size tubes. The interface with the centrifuge remains the same.
Regardless of the nature of the sample, the above described assemblage is fully functional. If the sample has been drawn into a tube with an anticoagulant, it remains a liquid and the distribution is as stated above. If the sample is drawn into a tube without an anticoagulant the blood clotting proteins will polymerize about the blood platelets which had previously agglutinated, and after a predetermined time say, for instance, 10 minutes, will form a gelatinous mass or blood clot. This mass is usually formed directly in the sample tube and centrifuged. Since the distribution of red cells and related material in the clot and the serum is essentially the same as that of the red cells and plasma in a liquid sample, the assemblage remains the same. Thus regardless of the nature of the specimen or sample, the simple arrangement described above is completely suitable for the task.
As will become apparent subsequently the entire system is designed around the disposables; two test tubes, a needle and a couple of stoppers. The fixture may also be disposable. The geometry is slender, easily handled and provides short sample separation times. Further the system is designed for automation particularly since assembly of the tubes, fixture, etc. is quite simple.
The above and other features, objects and advantages of the present invention, together with the best means contemplated by the inventors for carrying out the invention will become more apparent from reading the following description of a preferred embodiment and perusing the associated drawings in which: